High-pressure valve

ABSTRACT

Disclosed in one aspect is a valve comprising (a) a valve body having a poppet valve chamber with an axis running there through; (b) a seat having a seat sealing surface, and a outer-seat surface, the seat located axially within the poppet valve chamber; and (c) a poppet having a poppet sealing surface, the poppet being located axially within the poppet valve chamber; wherein a poppet-seat interface is created between at least a portion of the seat sealing surface and at least a portion of the poppet sealing surface, the poppet-seat interface being at an angle β of from 20 to 90° to the axis. In one embodiment the seat is removable, allowing the geometry of at least the poppet head surface and/or the seat inside surface, which defines a fluid flow-path cross-section, to be tailored.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of co-pending U.S. patentapplication Ser. No. 12/024,543, filed Feb. 1, 2008, and entitled“High-Pressure Valve,” the disclosure of which is hereby incorporated byreference herein.

FIELD OF THE INVENTION

The present invention relates in general to a valve useful for fluidchanneling, and more particularly to poppet valves comprising a seatthat creates a flow restriction zone to maintain adequate operation ofthe valve when traveling between the closed and the open position.

BACKGROUND OF THE INVENTION

High pressure ethylene compression, especially at pressures of between130 MPa and 350 MPa, is commonly employed in high pressure polyethyleneproduction. So called “hypercompressors” are used to achieve such highpressures, the fluid ethylene becoming a “supercritical fluid” at suchpressures. Poppet valves are commonly used on such hypercompressors. Thehypercompressor reliability is typically the largest source ofunreliability in the high pressure polymerization unit. In particular,the poppet valve life is one of the largest sources of unreliability ofthe hypercompressor. This unreliability is mainly due to wear of thepoppet valves.

Furthermore, and perhaps leading to such high unreliability,hypercompressor valve poppets often do not open and close duringoperation as desired. The forces that are created by the supercriticalfluid flow through the valve act upon the poppet during operation whichcauses the poppet to behave undesirably. The force which causes theundesirable behavior is an axial force created by a local low pressurezone between the seat and poppet sealing surfaces. Increasing the flowrate also increases the closing force on the poppet so that the poppetdoes not move to the open position with increasing flow rate.

What is needed is a means by which high pressure polymerizationprocesses can be run more reliably with less down time and less expensein replacing poppet valves in the hypercompressor. The inventors havesolved this and other problems in the design of a novel seat, preferablya replaceable seat, with a radial restriction between the poppet and theseat which is incorporated into a typical poppet valve design. Theradial restriction is a novel concept to enable the poppet positionduring operation to be a function of the fluid flow conditions throughthe valve. This solves the problem of unwanted poppet behavior due tothe forces created by fluid flow between the poppet and seat sealingsurfaces. The replaceable feature enables the introduction of the seatwith the novel radial restriction profile in existing valve bodies, andsimplified replacement of the valve.

SUMMARY OF THE INVENTION

In one aspect is a valve comprising (a) a valve body having a poppetvalve chamber and an axis running there through; (b) a seat having aseat inside surface, the seat located within the poppet valve chamber;and (c) a poppet having a poppet head surface, the poppet being locatedwithin the poppet valve chamber and capable of making contact with atleast a portion of the seat inside surface; and (d) a velocityincreasing means to provide a local high velocity zone adjacent to atleast a portion of the poppet head surface and at least a portion of theseat inside surface.

In another aspect is a valve comprising (a) a valve body having a poppetvalve chamber with an axis running there through; (b) a seat having aseat sealing surface, and a outer-seat surface, the seat locatedcoaxially within the poppet valve chamber; and (c) a poppet having apoppet sealing surface, the poppet being located coaxially within thepoppet valve chamber; wherein a poppet-seat interface is created betweenat least a portion of the seat sealing surface and at least a portion ofthe poppet sealing surface, the poppet-seat interface being at an angleβ of from 20 to 90° to the axis.

In another aspect is a hypercompressor valve comprising (a) a valve bodyhaving a poppet valve chamber with an axis running there through; (b) aseat having a seat inside surface and a outer-seat surface, the seatlocated coaxially within the poppet valve chamber; and (c) a poppethaving a poppet head surface, the poppet being located coaxially withinthe poppet valve chamber; wherein the seat is replaceable.

In yet another aspect is a process of channeling (or diverting) a fluidcomprising (a) providing a valve body having a poppet valve chamber withaxis running there through; (b) providing a seat having a seat sealingsurface, the seat located co-axially within the poppet valve chamber;and (c) providing a poppet having a poppet sealing surface, the poppetbeing located coaxially within the poppet valve chamber; wherein thevalve has an open position and a closed position, and wherein a flowrestriction zone is created adjacent to at least a portion of the poppetsealing surface in the range of poppet travel between the closedposition and the open position such that fluid flowing through the valvechamber and past the poppet in the open position creates a local highfluid velocity zone.

In yet another aspect is an olefin polymerization process comprisingproviding one or more compressors comprising one or more valvescomprising (a) a valve body having a poppet valve chamber with axisrunning there through; (b) a seat having a seat sealing surface, theseat located co-axially within the poppet valve chamber; and (c) apoppet having a poppet sealing surface, the poppet being locatedcoaxially within the poppet valve chamber; wherein the valve has an openposition and a closed position, and wherein a flow restriction zone iscreated adjacent to at least a portion of the poppet sealing surface inthe range of poppet travel between the closed position and the openposition such that fluid olefin flowing through the valve chamber andpast the poppet in the open position creates a local high fluid velocityzone.

As will be understood, the various features of these and other aspectsof the invention can be combined with the various embodiments of theinvention as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of one embodiment of the inventive valvefrom the downstream perspective, the individual parts separated to showdetails;

FIG. 2 a shows a close-up cross-section of the poppet in its openposition relative to the seat of the valve;

FIG. 2 b shows a close-up cross-section of the poppet in its openposition relative to the seat of the valve, and highlighting the flow offluid through the valve;

FIG. 2 c shows a close-up cross-section of the poppet in its closedposition relative to the seat of the valve;

FIG. 3 shows another cross-section of one embodiment of the inventivevalve from the upstream perspective, the individual parts separated toshow details;

FIG. 4 highlights the details of the seat, which is removable in oneembodiment;

FIG. 5 shows a cross-section of one embodiment of the inventive valve inthe closed position and showing how the components fit together;

FIG. 6 is a graphical representation of the lift (mm) of the poppet in atest valve as a function of differential pressure across the valve; and

FIG. 7 is a graphical representation of the lift (mm) of the poppet in atest valve as a function of fluid flow across the valve.

DETAILED DESCRIPTION OF THE INVENTION

An aspect of the invention is directed to a valve, more particularly avalve for use in high pressure devices such as a compressor, and mostparticularly a hypercompressor valve for use in a high pressurepolymerization reactor containing supercritical fluids. The valve is apoppet valve in one embodiment and comprises a seat that creates a flowrestriction of the operating fluid at and around the outside diameter ofthe head of the poppet as the fluid flows adjacent to the seat, and in aparticular embodiment, between the seat and the poppet. Each of the seatand poppet have at least one corresponding mating surface that creates aseal in the closed configuration of the valve. In the openconfiguration—any point between completely closed and up to andincluding fully open—there is at least one surface on each of the seatand poppet whose profile creates the flow restriction, altering thevelocity of fluid as it passes through the open valve. This flowrestriction, axisymmetric flow restriction zone in one embodiment, isslightly more of a restriction than the restriction created between thepoppet head and inside valve surface alone. The radial flow restrictioncreates a local high fluid velocity zone, which creates a greaterdifference in pressure between the upstream and downstream sides of thepoppet. In addition, the local low pressure zone that normally existsbetween the poppet and inside valve surface (without the added seat) isdisrupted. Since the restriction is radial (at the outside diameter ofthe poppet), the fluid forces on the poppet from this restriction areradially balanced.

Stated another way, in one embodiment of the invention is a velocityincreasing means that provides a local high fluid velocity zone at leastbetween the poppet head surface (located on the poppet) and the seatinside surface (located on the seat). The poppet head surface and seatinside surface face one another in a preferred embodiment. The result isa poppet that increases in lift (more open) as the flow rate of fluidsincreases.

More particularly, described herein is a valve comprising a valve bodyhaving a poppet valve chamber; a seat having a seat inside surface, theseat located within the poppet valve chamber; and a poppet having apoppet head surface, the poppet being located within the poppet valvechamber and capable of making contact with at least a portion of theseat inside surface; and further comprising a velocity increasing meansto provide a local high fluid velocity zone at least adjacent to thepoppet sealing surface and the seat sealing surface. In one embodiment,the velocity increasing means comprises a “flow restriction zone”defined by the profile of the seat inside surface and the poppet headsurface. These surfaces can take on any profile, the profile onlylimited in design in its capacity to create the flow restriction zone: alocal high fluid velocity zone created by the movement of fluid throughthe flow restriction. In the closed position of the valve, the poppethead surface and seat inside surface create a seal that stops fluid flowthere through.

Advantageously, the geometry that creates the flow restriction—theprofile of the poppet head surface relative to the profile of the seatinside surface—is such that it is a variable restriction; in oneembodiment the movement of the poppet itself as it opens and closesalong the axis of symmetry changes the velocity within the flowrestriction. The profile of the radial restriction that is formedadjacent to the seat is such that the amount of restriction changes asthe poppet moves in the range of poppet travel between the closedposition and the fully open position. Thus, the poppet position isdependent upon the flow rate of fluid through the valve and the amountof restriction between the poppet head and seat. The profile of theradial restriction can be manipulated to achieve the desired poppetposition at a given fluid flow rate. In particular, the radialrestriction is manipulated by adjusting the geometry, (angle and/orsurface area and/or diameter) of the seat inside surface and poppet headsurface.

In certain embodiments, the seat is removable. A replaceable seat isintroduced to the valve to enable the addition or adjustment of theradial restriction without having to purchase new valve bodies. By“replaceable,” what is meant is that the seat is not affixed within thevalve, as by welding, bolting, adhesive bonding or any other means. Thereplaceable seat is novel in that it possesses a conical sealing surfacethat seals against the inner valve body surface which distributes thestress in the valve body resulting from the contact force in a way tominimize stress concentration and enhance fatigue life. An additionalfeature of the replaceable seat is that refurbishment of the whole valvefor reuse is simplified by replacing the seat (the wear item) instead ofmachining a deeper seat profile in the valve body. This feature greatlyincreases the number of times a valve body can be reused. Thus, thereplaceable seat design decreases maintenance cost.

One embodiment of the invention will be described with respect to theFIGS. 1-5. First referring to FIG. 1 is a valve body 101 having at leastone poppet valve chamber 103. Contained and seated within the poppetvalve chamber 103 is a seat 109, preferably located and seated againstvalve inside surface 105. In one embodiment, the valve inside surface105 is conical in shape, mating with the outer-seat surface 137 andcreating a fluid seal when the poppet is in the closed position, as inFIG. 2 c. In a preferred embodiment, the seat 109 is replaceable.

For ease of reference, the poppet valve chamber 103 is referenced aspossessing an axis 107 which forms an axis of symmetry through thecylindrically-shaped chamber 103. The poppet is located coaxially withinthe poppet valve chamber 103. The seat 109 comprises a seat insidesurface 151 (FIG. 4). The seat inside surface is preferably axisymmetricabout the seat, and in one embodiment comprises at least one seatsealing surface 111 and at least one flow restriction surface 113. In apreferred embodiment, there is only one seat sealing surface 111 and oneflow restriction surface 113. In one embodiment, the seat 109 comprisesa seat sealing surface 111 and a flow restriction surface 113 (FIGS. 1and 4) that are distinct from one another, meaning that they each mayhave a different angle or shape relative to axis 107 and/or one another.At least one surface, the seat sealing surface 111 in a preferredembodiment, forms a fluid seal with the poppet when the poppet is in theclosed position as in FIG. 2 c.

The poppet 115 comprises a poppet head surface 153, preferablyaxisymmetric about the poppet. The poppet head surface comprises apoppet sealing surface 119 and a second poppet surface 149 in aparticular embodiment. In one embodiment, the poppet 115 comprises apoppet sealing surface 119 and a second poppet surface 149 that aredistinct from one another, meaning that they each may have a differentangle or shape relative to axis 107 (FIG. 2) and/or each other. In oneembodiment, the seat sealing surface 111 faces the poppet 115 having apoppet sealing surface 119. In one embodiment, the poppet sealingsurface 119 forms a fluid seal with the seat, preferably with the seatsealing surface 111, when the poppet is in the closed position as inFIG. 2 c.

The poppet sealing surface 119 makes at least partial contact,discontinuous around the circumference in one embodiment, and continuouscontact in another embodiment, with at least the seat sealing surface111 such that when the valve is in a closed position a poppet-seatinterface 143 (FIG. 2 c) is created. Upon opening (the poppet travelsupward or away from orifice 135), a flow restriction zone 121 is createdgenerally between the seat inside surface 151 and the poppet headsurface 153. In the embodiment in FIGS. 1-5, the restriction is createdby the intersection of poppet sealing surface 119 and the second poppetsurface 149, those surfaces being at distinct angles from one anotherrelative to the axis 107, thus creating a “pinch” point or narrowed zonebetween the seat and poppet. Fluid rushing past the poppet is then“pinched”, which generates a high fluid velocity zone. This high fluidvelocity zone can be manipulated by the geometry (cross-sectional shape)of the flow restriction zone, which in turn is adjusted by the design ofat least the flow restriction surface 113, the poppet sealing surface119, or the second poppet surface 149, or a combination of each.

The valve and its components can be made using any material (e.g.,metal, alloy, ceramic, combination thereof) that can withstand theworking pressures of a hypercompressor. The components of the valveassembly are made from high strength steel or ceramic in one embodiment,preferably high strength steel. In certain embodiments, the valve bodyis made of high strength steel, and the seat, compression sleeve andpoppet are made of ceramic or high strength steel, preferably highstrength steel.

Referring still to the Figures, fluid, supercritical fluid in oneembodiment, flows down a valve channel as in flow A and into the valvechamber 103 through orifice 135 as in flow C. The flow of fluid thenenters the poppet valve chamber 103 at the upstream end 125 (FIGS. 1 and2 b) of the poppet valve chamber 103, and through the chamber when thevalve is in the open position (as in FIG. 2 b) and out of the poppetvalve chamber 103 as fluid flow B out the downstream end 127 of thepoppet valve chamber. The seat 109 is generally an axisymmetric shapethat fits at the upstream end 125 of poppet valve chamber 103 of a valvebody 101. The seat 109 has an outer-seat surface 137 in one embodimentthat contacts the mating valve inside surface 105 at the upstream end125 of the poppet valve chamber 103. The outer-seat surface 137 (FIG. 3)may be lapped to the inside valve surface 105 to enhance a metal tometal seal at the valve-seat interface 147 (FIG. 5). The poppet 115located downstream of the seat 109 has a poppet head 123 that actsagainst the replaceable seat 109 to create the poppet-seat interface 143(FIG. 2 c). In one embodiment, the seat 109 has a seat sealing surface111 that mates against at least the poppet sealing surface 119 to form apoppet-seat interface 143 when the poppet valve is in the closedposition (FIG. 2 c). These surfaces 111 and 119, creating thepoppet-seat interface 143 when the poppet valve is in the closedposition, form an angle β (FIG. 2) with respect to the axis 107 withinthe range of from 20 to 90° in one embodiment, and from 25 to 85° inanother embodiment, and from 30 to 80° to the axis in one embodiment,and from 35 to 75° in another embodiment, and from 45 to 75° in yetanother embodiment, wherein any upper limit can be combined with anylower limit to create a desirable range.

Further, a valve-seat interface 147 (FIG. 5) is located at theouter-seat surface 137 contacting the valve inside surface 105, thevalve-seat interface 147 also being at an angle β′, wherein β′ may bethe same or different angle from β. The angle β′ with respect to theaxis 107 is within the range of from 20 to 90° in one embodiment, andfrom 20 to 85° in another embodiment, and from 30 to 80° to the axis inone embodiment, and from 35 to 75° in another embodiment, and from 45 to75° in yet another embodiment. The valve-seat interface 147 serves as asealing interface to prevent higher pressure fluid located at thedownstream end of the valve and in the chamber from communicating to theupstream end of the valve 125 when the valve is in the closed position.The force created from the differential pressure downstream and upstreamof the valve while the valve is in the closed position acts against theseat 109 which reinforces the fluid sealing properties of the valve-seatinterface 147. This force creates stress in the valve body 101. Thisstress is distributed from the valve surface 105 into the valve body101. The valve-seat interface 147 can be optimized by adjustments in theangle β′ of the conical inside valve surface 105 and the surface 137thereby preventing undesirable stress concentrations within the valvebody 101 in the vicinity of the seat.

The seat 109 is held in position at least in part by a compressionsleeve 117 (FIGS. 1, 3 and 5) that contacts a shoulder 139 (FIG. 4) onthe downstream end of the seat 109. The upstream end of the compressionsleeve 117 contacts this shoulder 139 adjacent to the outside diameterof the seat 109. The compression force of the compression sleeve 117 isachieved, in one embodiment, by an axial interference fit within thepoppet valve chamber 103, thereby achieving a force acting parallel toaxis 107 to hold the seat in position.

As mentioned, there is a flow restriction zone 121 created between thepoppet head 123 and the seat 109 at least adjacent to the surface 113 inone embodiment, and also adjacent to second poppet surface 149 inanother embodiment. This flow restriction zone 121 is, in one aspect ofthe invention, advantageous to the proper function of the poppet 115performance. The flow restriction zone 121 is such that the greatestrestriction of fluid through the valve (smallest cross section area offlow) occurs at this flow restriction zone 121, between at least theflow restriction surface 113 and the poppet sealing surface 119 duringmost of the poppet range of travel. In a particular embodiment, the flowrestriction zone 121 is also adjacent to second poppet surface 149 (FIG.2 a). A flow restriction surface 113, which is substantially conical inone embodiment of the seat 109, defines the outer profile of flowrestriction zone 121 while the edge (or edge feature) defined by theintersection of poppet sealing surface 119 and second poppet surface 149of the poppet head 123 defines in part the inner profile of flowrestriction zone 121. The shape of the flow restriction surface 113 issuch that as the poppet 115 travels to the fully open position (FIG. 2a), the open area increases and, thus, the restriction of the radialflow restriction zone 121 is reduced. The opposite occurs as the poppet115 travels to the fully closed position (FIG. 2 c). The cutaway view ofone embodiment of the valve in FIG. 2 b highlights how the fluid flow Cchannels into the valve chamber 103 through orifice 135 and around thepoppet head 123 and out through the downstream end 127.

The geometry, or profile, of the poppet 115, and in particular, thepoppet head 123 can take on various forms, as long as there is at leastone surface that sealingly mates with the inside surface of the seatsuch as to create a seal when the poppet is in the closed position, notallowing the flow C to enter the valve chamber; and also, the profilecan take any form as long as a flow restriction zone is created.Likewise, the inside surface of the seat (comprising surfaces 111 and113 in the embodiment in the Figures) can also take on any geometry, aslong as there is at least one mating surface that creates a seal with atleast a part of the surface of the poppet; and also, the profile cantake any form as long as a flow restriction zone is created.

More particularly, the poppet-seat interface 143, formed by the sealingcontact of at least surfaces 111 and 119, is not limited to the geometryshown in the Figures, but can take on any geometry. For example, theseat sealing surface 111 might be curved in a concave direction, whilepoppet sealing surface 119 could be correspondingly convex. Also,surfaces 111 and 113 together could be continuous, excluding the channel129, or could together form different geometries. The channel, ifpresent, can also take on various forms such as having a deeper profile,or wider, or narrower. Also, the flow restriction surface 113 could takeon a curved or other more complex profile.

Note that for simplicity of illustration, the valve body as shown (e.g.,FIG. 5) in the illustrated embodiment is without any form or materialwhich would encompass or surround the full length of the compressionsleeve 117. The valve body 101 would, in a preferable embodiment, extendoutward to encompass at least the full length of the compression sleeve117. Thus, the inside wall of the poppet valve chamber 103 extends, in apreferred embodiment, the length of the compression sleeve 117,intimately contacting the outer sleeve surface 133 (FIG. 3), while theinside sleeve surface 131 makes up the full length of the poppet valvechamber 103.

In certain embodiments, the seat 109 possesses a pressure balancingmeans 141, shown more fully in one embodiment in FIG. 4, to communicatefluid between at least the outside seat surface 145 of the seat 109 tothe inside surface made up at least by seat sealing surface 111 and flowrestriction surface 113, and in one embodiment the groove 129 therebetween, of the seat 109 to prevent unwanted differential pressureforces acting upon the seat. The pressure balancing means 141 may be inthe form of a groove in one embodiment, or a hole running through thethickness of seat 109 in another embodiment, or other shape.

The valves described herein are particularly useful in compressors,“hypercompressors” in a particular embodiment, which is a compressorthat maintains a fluid from at least 80 or 100 MPa or more of pressure.Typically, the inventive valves reside in the final stagehypercompressor that supplies a high pressure polyethylene (“HP-PE”)reactor with the process fluid. For example, one reactor linehypercompressor may have 4, 6, 8, or 10 cylinders in the final stagewith these valve assemblies, and each valve assembly may have two poppetvalves, so there are total of at least 8 to 20 poppet valves. In theHP-PE process of this invention the temperature of the medium withinwhich the polymerization reaction occurs is at least 140° C., andpreferably above 160° C., and may range up to just below thedecomposition temperature of polyethylene product in another embodiment;and ranges to a temperature within the range of from 140 to 350° C. inyet another embodiment; and within the range from 180 to 280° C. in yetanother embodiment. In one embodiment, the polymerization is completedat a pressure above 50 MPa, and at above a pressure of 100 MPa inanother embodiment, and at a pressure of within the range from 50 to 350MPa, and at a pressure within the range from 80 to 150 MPa in yetanother embodiment.

One embodiment of the high-pressure polyolefin polymerization process isdescribed here. In its most preferred embodiments, the high-pressurepolymerization process is carried out as a continuous process. As such,the polymerization medium (containing polymer product and catalyst) isremoved from the reaction zone where fresh catalyst (e.g., radicalgenerator, or organometallic compound, metallic coordination compound,or combination thereof), monomer and, and when present, a diluent, areadded to the reaction zone in corresponding amounts to maintain anequilibrium of mass within the reaction zone. In the continuous process,unreacted monomer and/or diluent are recovered from the polymer productby flash evaporation, conditioned for reuse and recycled to the reactionzone as at least a part of the makeup amounts of monomer and/or diluentfeed to the reaction zone. To save cost of recompression of recoveredmonomer it is preferably flashed away from the product polymer by only aslight reduction of pressure, or, alternatively with no reduction ofpressure by the addition of moderate amounts of additional heat to themedium during the flash recovery operation. When a polymerizationdiluent is used as the medium, the bulk of unreacted monomer ispreferably recovered separately from the diluent by a first highpressure flashing operation and the diluent, together with small amountsof unreacted monomer, is next recovered by total pressure reduction onthe medium.

As indicated, the polymerization of monomers occurs in a medium whichcarries the catalyst into contact with the monomer and absorbs the heatof reaction liberated by monomer polymerization. The polymerizationmedium may comprise a normally fluid inert hydrocarbon compound or themedium may consist essentially of a normally gaseous monomer which underapplication of pressure is preferably maintained in a supercriticalfluid state within the reaction zone. The hypercompressors maintain thesupercritical state by delivering the reactor feed gas in a continuousmode from the primary compression and recycle systems of a HP-PE unit.One embodiment of the valves of the invention act within thehypercompressor during the reciprocating motion of the hypercompressorto direct the flow of fluid into the cylinder from the fluid inletduring the suction stroke and out of the cylinder to the outlet duringthe discharge stroke without incurring backflow of fluid duringoperation. Thus, the valves work as suction and discharge check valveswithin the hypercompressor cylinders.

Generally, when a normally fluid inert hydrocarbon is used to providethe reaction medium, the polymerization reaction may be carried out atlower pressures than required when the polymerization medium consistsessentially of a fluidized monomer, ethylene in a particular embodiment.When present, inert hydrocarbon compounds which may be used as apolymerization diluent to provide the polymerization medium includealiphatic, cycloaliphatic, and aromatic hydrocarbons having from six totwenty carbon atoms.

More preferably, the process is practiced with a polymerization mediumwhich consists essentially of one or more monomers—one or more C₂ to C₁₀olefins in one embodiment, and ethylene and an optional C₂ to C₁₀α-olefin in a particular embodiment—maintained by added pressure in asupercritical fluid state. The four or more hypercompessors maintain themonomers (and, if present, diluent) in the supercritical state,preferably at a pressure of at least 100 MPa, and at least 130 MPa inanother embodiment. Although this entails a greater degree of initialmonomer compression and compression cost, this method of practice ispreferred because no portion of the reactor volume is occupied by aninert diluent compound. Thus, with the same reactor, a greater level ofthroughput of polymer production can be realized than when an inertdiluent is used as the polymerization medium.

Thus, one aspect of the invention is directed to a high pressurepolymerization process comprising channeling a fluid, where a valve bodyhaving a poppet valve chamber is provided; providing a seat having aseat sealing surface, the seat located within the poppet valve chamber;and providing a poppet having a poppet sealing surface, the poppet beinglocated within the poppet valve chamber and capable of making contactwith the seat sealing surface; and further comprising a flow restrictionmeans to provide a local high velocity zone at least between the poppetsealing surface and the seat sealing surface. Olefin monomers, primarilyethylene in one embodiment, are supplied to the hypercompressor underpressure such that the monomers are in a supercritical state, thesupercritical fluid is further pressurized in the hypercompressor(s) andthe supercritical fluid passes through the valve body as through path Aand into orifice 135 as through path C, lifting the poppet from the seatduring each stroke of the reciprocating compressor cylinder, whereby thesupercritical monomers can then pass as through path B out thedownstream end 127 of the poppet valve chamber 103.

A particular aspect of the invention is directed to a valve comprising avalve body having a poppet valve chamber; a seat having a seat insidesurface 151, the seat located coaxially within the poppet valve chamber;and a poppet having a poppet head surface 151, the poppet being locatedcoaxially within the poppet valve chamber and capable of making contactwith the seat inside surface; and further comprising a velocityincreasing means to provide a local high velocity zone at least adjacentto the poppet head surface 151 and the seat sealing surface. In oneembodiment, the velocity increasing means is provided by the geometry ofthe poppet and seat; such geometry being defined by the cross-sectionalprofile of the poppet head surface and seal inside surface. In oneembodiment, the velocity increasing means comprises a flow restrictionzone defined by the profile of the seat inside surface and the profileof the poppet head surface. In a particular embodiment, a poppet-seatinterface is created between the seat inside surface and the poppet headsurface, the poppet-seat interface being at an angle β of from 20 to 85or 90° to the axis. In yet another embodiment, the poppet head surfacefurther comprises a flow restriction surface 113 and a second poppetsurface 149, wherein a flow restriction zone is located at leastadjacent to the flow restriction surface and the poppet sealing surface.In another embodiment, the valve has an open position and a closedposition, and partially open positions in between, and wherein there isa flow restriction zone adjacent to at least the flow restrictionsurface except for the closed position.

In a preferable embodiment, the seat is removable from the valve body,meaning that it is not permanently fixed to the valve body but can beremoved and/or replaced by a new seat or a refurbished seat. The onlycriteria is that conical surface 137 that creates the sealing interface147 should be nearly the same or identical to the seat being replacedfor the same valve body, as the sealing interface will be determined atleast in part by the shape of the inside valve surface 105 that willtypically remain fixed.

In a particular embodiment, the flow restriction zone has a flow pathcross sectional area that is less than the flow path cross sectionalarea between the poppet sealing surface and the seat sealing surface fora given position of the poppet in an open position. This occurs in oneembodiment when the poppet head surface is discontinuous such that thereis an edge or “pinch point” created by the poppet head, this pinchpoint, and the facing seat inside surface, creates the flow restrictionzone. In a more particular embodiment, the seat inside surface comprisestwo discontinuous surfaces—a seat sealing surface and a flow restrictionsurface, the flow restriction surface participating in the creation ofthe flow restriction zone as the poppet travels to the fully openposition. In yet a more particular embodiment, the geometry of thepoppet head (which can comprise one surface, or two or more surfaces atdifferent angles from one another) and the seat inside surface (whichcan comprise one surface, or two or more surfaces at different anglesfrom one another) is such that the fluid-velocity enhancement of theflow restriction zone is stronger when the poppet is near the closedposition, and small or negligible when the poppet is in the fully openposition.

EXAMPLE

A test of an embodiment of the valve of the invention was performed inthe laboratory, the results of which are shown in FIGS. 6 and 7. Asimulated compressor head and valve body was constructed, having a meansfor measuring fluid volume flow rate, pressure upstream and downstreamof the valve and the poppet position. Water was used as the operatingfluid as its properties are close to supercritical ethylene (essentiallyincompressible, that is ρ/ρo nearly equal to 1).

Having described aspects of the invention in some detail, in a firstnumbered embodiment:

-   (1) is a valve comprising:    -   (a) a valve body having a poppet valve chamber with an axis        running there through;    -   (b) a seat having a seat sealing surface, and a outer-seat        surface, the seat located axially within the poppet valve        chamber; and    -   (c) a poppet having a poppet sealing surface, the poppet being        located axially within the poppet valve chamber;    -   wherein a poppet-seat interface is created between the seat        sealing surface and the poppet sealing surface, the poppet-seat        interface being at an angle β of from 20 to 85° to the axis.-   2. The valve of numbered embodiment 1, wherein a valve-seat    interface is located between the outer-seat surface and the valve    inside surface, the valve-seat interface being at an angle β′ of    from 20 to 90° to the axis.-   3. The valve of numbered embodiments 1 and 2, wherein the poppet    sealing surface further comprises a flow restriction surface that is    distinct from the poppet sealing surface, wherein a flow restriction    zone is located adjacent to the flow restriction surface and the    seat sealing surface.-   4. The valve of any of the preceding numbered embodiments, wherein    the valve has an open position and a closed position, and partially    open positions in between, and wherein there is a flow restriction    zone adjacent to at least the flow restriction surface except for    the closed position.-   5. The valve of any of the preceding numbered embodiments, wherein    the flow restriction zone has a flow path cross sectional area that    is less than the flow path cross sectional area between the poppet    sealing surface and the seat sealing surface for a given position of    the poppet in an open position.-   6. The valve of any of the preceding numbered embodiments, wherein    the seat also possesses seat outside seat surface adjacent to the    inside wall of the poppet valve chamber.-   7. The valve of any of the preceding numbered embodiments, wherein    the seat possesses a pressure balancing means, fluidly communicating    between the surfaces and the poppet valve chamber.-   8. The valve of any of the preceding numbered embodiments, wherein    the seat is removably contacting the inside valve inside surface.-   9. The valve of any of the preceding numbered embodiments, wherein    the seat possesses an outer-seat surface that removably contacts the    inside valve inside surface.    10. The valve of any of the preceding numbered embodiments, further    comprising a compression sleeve compressively contained within the    poppet valve chamber and adjacent to the seat.-   11. The valve of any of the preceding numbered embodiments, wherein    the valve operates under a pressure differential in the closed    position of at least 80 MPa.-   12. A compressor comprising the valve of any of the preceding    numbered embodiments.-   13. A process of channeling a fluid of any of the preceding numbered    embodiments, comprising:    -   (a) providing the valve body having a poppet valve chamber with        an axis running there through;    -   (b) providing the seat having a seat sealing surface, the seat        located co-axially within the poppet valve chamber; and    -   (c) providing the poppet having a poppet sealing surface, the        poppet being located axially within the poppet valve chamber;    -   wherein the valve has an open position and a closed position,        and wherein a flow restriction zone is created adjacent to at        least the poppet sealing surface in the range of poppet travel        between the closed position and the open position such that        fluid flowing through the valve chamber and past the poppet in        the open position creates a local high fluid velocity zone.-   14. The process of numbered embodiment 13, wherein the fluid is a    supercritical fluid.-   15. The process of numbered embodiments 13 and 14, wherein the flow    restriction zone has a flow path cross sectional area that is less    than the flow path cross sectional area between the poppet sealing    surface and the seat sealing surface.-   16. The process of numbered embodiments 13 through 15, wherein the    flow restriction zone is located radially out from the poppet.-   17. An olefin polymerization process comprising providing one or    more compressors comprising one or more valves of any of the    preceding numbered embodiments comprising:    -   (a) a valve body having a poppet valve chamber with an axis        running there through;    -   (b) a seat having a seat sealing surface, the seat located        co-axially within the poppet valve chamber; and    -   (c) a poppet having a poppet sealing surface, the poppet being        located axially within the poppet valve chamber;    -   wherein the valve has an open position and a closed position,        and wherein a flow restriction zone is created adjacent to at        least the poppet sealing surface in the range of poppet travel        between the closed position and the open position such that        fluid olefin flowing through the valve chamber and past the        poppet in the open position creates a local high fluid velocity        zone.-   18. The process of any of the preceding numbered embodiments,    wherein the seat is removable.

In another aspect is the use of a valve in a polyolefin polymerizationreactor, the valve comprising (a) a valve body having a poppet valvechamber and an axis running there through; (b) a seat having a seatsealing surface, the seat located within the poppet valve chamber; and(c) a poppet having a poppet sealing surface, the poppet being locatedwithin the poppet valve chamber and capable of making contact with theseat sealing surface; and (d) a velocity increasing means to provide alocal high velocity zone adjacent to the at least one poppet sealingsurface and the at least one seat sealing surface.

In another aspect is the use of a valve in a polyolefin polymerizationreactor, the valve comprising (a) a valve body having a poppet valvechamber with an axis running there through; (b) a seat having a seatsealing surface, and a outer-seat surface, the seat located axiallywithin the poppet valve chamber; and (c) a poppet having a poppetsealing surface, the poppet being located axially within the poppetvalve chamber; wherein a poppet-seat interface is created between atleast a portion of the seat sealing surface and at least a portion ofthe poppet sealing surface, the poppet-seat interface being at an angleβ of from 20 to 90° to the axis.

What is claimed is:
 1. A compressor check valve comprising: (a) a valvebody having a poppet valve chamber with an axis running there throughand a valve inside surface; (b) a removable seat having a seat sealingsurface, a flow restriction surface and an outer-seat surface, the seatlocated axially within the poppet valve chamber; and (c) a poppet havinga poppet sealing surface and a second poppet surface each having adifferent angle relative to the axis, and wherein the poppet sealingsurface and the second poppet surface form an intersection, and whereinthe location of the poppet is dependent on the flow rate of a fluidthrough the valve, the poppet being located axially within the poppetvalve chamber; wherein the intersection and the flow restriction surfaceare operable to form a flow restriction zone for fluid flowingtherebetween, wherein a poppet-seat interface is created between theseat sealing surface and the poppet sealing surface, the poppet-seatinterface being at an angle β of from 20° to 90° to the axis, andwherein the compressor check valve further comprises a compressionsleeve compressively contained within the poppet valve chamber andadjacent to the seat.
 2. The valve of claim 1, wherein a valve-seatinterface is located between the outer-seat surface and the valve insidesurface, the valve-seat interface being at an angle β′ of from 20° to90° to the axis.
 3. The valve of claim 2, wherein the seat is operableto removably contact the valve inside surface.
 4. The valve of claim 2,wherein the seat possesses an outer-seat surface that is operable toremovably contact the valve inside surface.
 5. The valve of claim 1,wherein the valve has an open position and a closed position, andpartially open positions in between, and the flow restriction zone isadjacent to at least the flow restriction surface except for the closedposition.
 6. The valve of claim 5, wherein the flow restriction zone hasa flow path cross sectional area that is less than a flow path crosssectional area between the poppet sealing surface and the seat sealingsurface for a given position of the poppet in an open position.
 7. Thevalve of claim 1, wherein the seat also possesses an outside seatsurface adjacent to the inside wall of the poppet valve chamber.
 8. Thevalve of claim 7, wherein the seat possesses a pressure balancing means,fluidly communicating between the outer-seat surface and an insidesurface made by the seat sealing surface and the flow restrictionsurface and the poppet valve chamber.
 9. The valve of claim 1, whereinthe valve operates under a pressure differential in the closed positionof at least 80 MPa.
 10. The valve of claim 1, wherein the valve is ahypercompressor check valve.